Why are MACHOs in the Halo not the disk

[Daniel_G]

Hi, I was just wondering, why are we only looking for massive compact HALO objects?

Can there not be such objects in the Galaxys disk, if so why? Or have simply already detected all of them, if so how?

 

[Vanadium 50]

Because we know there's unobserved material in the halo. So it makes sense to look for them there.

 

[Daniel_G]

I only know of reasons for there being unobserved matter distributed over the galaxy, how do you know it is in the halo?

 

[Vanadium 50]

Because the rotation curves are not sensitive to extra matter near the core.

 

[Daniel_G]

I never asked for why the matter is at large radii.

I just realized that maybe the disk is considered part of the Halo, and therefore any dark matter in the disk is also in the halo. So halo objects may just as well be in the disk, right?

 

[Vanadium 50]

No, you asked why people are *looking* at large radii. That's the answer. Maybe they are in the disk too, maybe not.

 

[d3mm]

Galaxies rotate. The speed of rotation should decrease as you approach the edge. However it remains relatively constant. The most likely explanation is there is a lot of mass in a halo around the galaxy outside of the visible disc, and it's dark so we can't see it with telescopes. So this is why people are looking for MACHOs.

 

[Daniel_G]

...there is a lot of mass in a halo around the galaxy outside of the visible disc...

I'm not confused about the existence of mass, but about the location. Why outside of the disk? why not in between visible Stars?

 

[d3mm]

That's where the equations say it must be to explain the rotation speed of the galaxy.